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Abstract: FR-PO022

Role of the Complement System and Vascular Endothelium in COVID-19 Pathogenesis

Session Information

Category: Coronavirus (COVID-19)

  • 000 Coronavirus (COVID-19)


  • Rostam Shirazi, Niyousha, University of Toronto, Toronto, Ontario, Canada
  • Licht, Christoph, The Hospital for Sick Children, Toronto, Ontario, Canada

Coronavirus Disease 2019 (COVID-19) caused by SARS-CoV-2 infection has become a global pandemic, presenting with varying degrees of severity from respiratory distress to multi-organ damage. Kidneys are of several organs affected in COVID-19, with acute kidney injury (AKI) being a common consequence, occurring in more than 30% of patients with severe COVID-19. While the underlying mechanisms of COVID-19 pathogenesis remain poorly understood, there is evidence linking complement system overactivation and endothelial injury to organ damage that increases the risk of mortality in COVID-19. Evidence from previous coronavirus epidemics also suggest direct involvement of inflammation, complement dysregulation, and endothelial cell dysfunction. Thus, we hypothesize that vascular endothelial injury resulting from complement overactivation contributes to COVID-19-associated organ injury.


Clinical information and sera from SARS-CoV-2+ patients with mild (n=7) and severe COVID-19 (n=7) diseases were obtained from the Canadian COVID-19 Prospective Cohort Study (CANCOV). Complement activation on ECs was evaluated via immunofluorescence assays, measuring the deposition of complement products C3b and C5b-9 on Human Umbilical Vein Endothelial Cells exposed to control or patient sera. In addition, a permeability assay using a transwell model was used to measure the integrity of the endothelial monolayer exposed to patient sera.


Complement was found to be overactivated on ECs treated with SARS-CoV-2+ patient sera compared to those treated with normal human serum as evidenced by significantly increased C3b and C5b-9 deposition. While ECs treated with sera from patients with mild COVID-19 seemed to have higher C3b deposition, ECs treated with sera from patients with severe COVID-19 disease were associated with higher C5b-9 deposition. In addition, increased permeability of the monolayer incubated with SARS-CoV-2+ patient sera was seen over time regardless of disease severity. However, ECs tretaed with severe COVID-19 patient sera had signficiantly increased vascular leakiness as evidenced by increased permeability of the treated monolayer.


Thus, we conclude that complement is overactivated in SARS-CoV-2+ patients and use of anti-complement therapies may be an effective strategy in treating COVID-19 associated vascular injury, hyperinflammation, and organ damage.